You're right. I have an RPD BC, and the feed stud is off-center to the left. It will take some engineering. I've had a few problems with the bolt & BC UNLOCKING - need to get that straightened out first. Most of the other build basics are falling into place nicely. Will be using a twin-spring set-up much like 2XTM's, but simpler to build, using UN-captured springs

The piston / gas tube set-up is well underway. You'll like it - pics will be coming along when I get time at home

here is mine so far, I am using one of my semi auto mg42 grip sticks with a fal fcg.
I bushed the rear hole so it mounts fron & back with HK forearm pins. next step is to install the feed stud and recoil spring. I am holding off on cutting the ejection port & retracting slot till I can get to a mill.

I am also working on drawings to get a couple receivers laser cut and bent if this turns out good. After looking at it I have come to the conclusion it really neds a set of spade grips in the back instead of a stock. I will try that after this one is working.

I found a supplier who carries 1 1/8" sq tubing in various wall thickness, that will fit the RPD TC latch - have been on the road but will post the name and link when I can. That size is difficult to come by

Are you going pistol or carbine? Pistol is real tricky gas-pressure-wise but I think I have it figured out and will post the 'trick pics' when I can

I wish I could weld as good as many of you can. I am envious but am practicing

Your build is really something. I hope you'll share more pics here as you go

OK now for my stupid question of the day.
I never thought about this until these belt fed builds started but what is the actual purpose of the upper left rail ( I know the right is for the ejector ) and I know it would be the same as the lower right in an AK, it doesn't seem to have any real purpose or does it?